Gypsum wallboard produced using a high water-to-stucco ratio

ABSTRACT

A gypsum composition, board, and method of producing a gypsum board with increased fire endurance are described. The set gypsum-containing composition can be used to prepare a gypsum board having fire endurance, based on particular water-to-stucco ratios.

BACKGROUND OF THE INVENTION

Gypsum products can be generally manufactured using a slurry formed from at least water and stucco. The stucco, which is calcium sulfate hemihydrate (CaSO₄.½H₂O), reacts with water to form gypsum, which is calcium sulfate dihydrate (CaSO₄.2H₂O). Gypsum wallboard can be a composite board comprising a core, face sheet, and back sheet. The density of gypsum wallboard can be reduced by adding aqueous foam to the stucco slurry in an amount effective to provide the desired gypsum core density. The volume of the wallboard is occupied by gypsum, packing voids of the gypsum crystals, voids left by evaporation of water (i.e., water voids), and voids generated by foam (i.e., foam voids). As the board contains less gypsum per unit volume, there is less crystallized water available to extend fire endurance of the wallboard. Gypsum wallboards are commonly used in drywall construction of interior walls and ceilings, and should be able to withstand both fire and excessive temperatures. As a result, gypsum wallboards are manufactured using specifications that maximize fire endurance/resistance.

Fire endurance/resistance of gypsum wallboard is measured by the period for which a board can withstand a standard fire test. The fire resistance of a wallboard is classified according to the ability for a wallboard to avoid an increase in temperature, flame passage, and structural collapse. In order to have various parties, including constructors, occupants, and regulating bodies, evaluate the fire endurance on a common basis, fire test assemblies are categorized into several standard arrangements. Some common assemblies include test designs defined by Underwriters Laboratories, Inc. (UL®), a testing and certification agency, which has tests that are referred to as U305, U419, and U423.

A standard fire test is customarily conducted in accordance with the requirements of ASTM E119. In such tests, a fire resistance classification can be established based on the time at which a wall assembly shows excessive temperature rise, or passage of flame, or structural collapse. Failure of the test occurs when the average temperature as measured by several thermocouples on the unexposed surface increases more than 250° F. above ambient temperature, or any individual thermocouple rises more than 325° F. above ambient temperature. The duration of fire endurance of a system is not only dependent upon the gypsum board used in the system, but also depends upon many other factors, including wall assembly thickness, stud type and spacing, board size, insulation type, and others.

Although existing techniques are useful in extending wallboard fire endurance and resistance, further improvement is always desirable.

BRIEF SUMMARY OF THE INVENTION

In one aspect, the present invention provides a fire resistant gypsum board comprising a set gypsum composition disposed between two cover sheets, the set gypsum composition comprising an interlocking matrix of set gypsum formed from a slurry comprising at least stucco and water. The slurry has a water-to-stucco ratio from about 0.7 to about 2.0. The fire resistant gypsum board has a density from about 24 lbs/ft³ to about 40 lbs/ft³, and when at a thickness of about % inch, a nail pull resistance of at least about 70 lbs of force as determined according to ASTM C473-09 (e.g., ASTM C473-09, method B), and a Fire Endurance Index (FEI) greater than about 52 minutes.

In another aspect, the present invention provides a fire resistant gypsum board comprising a set gypsum composition disposed between two cover sheets, the set gypsum composition comprising an interlocking matrix of set gypsum formed from a slurry comprising at least stucco and water, and having a water-to-stucco ratio from about 1.2 to about 2.0. The fire resistant gypsum board has a density from about 24 lbs/ft³ to about 40 lbs/ft³, and when at a thickness of about % inch, a nail pull resistance of at least about 70 lbs of force as determined according to ASTM C473-09 (e.g., ASTM C473-09, method B), and a Fire Endurance Index (FEI) greater than about 54 minutes.

In yet another aspect, the present invention provides a method for making a fire resistant gypsum board comprising forming a slurry of at least stucco and water. The slurry has a water-to-stucco ratio from about 0.7 to about 2.0. The gypsum stucco slurry is deposited on a sheet to create a board preform. The board preform is cut into predetermined dimensions after the slurry has hardened sufficiently for cutting. The board is dried. The fire resistant gypsum board has a density from about 24 lbs/ft³ to about 40 lbs/ft³, and when at a thickness of about ⅝inch, a nail pull resistance of at least about 70 lbs of force as determined according to ASTM C473-09 (e.g., ASTM C473-09, method B), and a Fire Endurance Index (FEI) greater than about 52 minutes.

These and other advantages of the present invention, as well as additional inventive features, will be apparent from the description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram displaying cross sections of low density gypsum boards in accordance with embodiments of the invention.

FIG. 2 is a diagram displaying the structure of the small scale test device used to determine the Fire Endurance Index (FEI) of a wallboard sample in accordance with embodiments of the invention.

FIG. 3 is a line graph displaying the temperature profile (Y-axis) over time (X-axis) of a furnace used during the small scale fire test illustrated in FIG. 2, in accordance with embodiments of the invention.

FIG. 4 is a line graph displaying a correlation between fire endurance of U419 test (Y-axis) and fire endurance of small-scale test of FIG. 2 (X-axis) in accordance with embodiments of the invention.

FIG. 5 is a line graph displaying the unexposed surface temperature (Y-axis) over time (X-axis) for wallboards of Example 1 during a small-scale fire test in accordance with embodiments of the invention.

FIG. 6 is a line graph displaying the unexposed surface temperature (Y-axis) over time (X-axis) for wallboards of Example 2 during a small-scale fire test in accordance with embodiments of the invention.

FIG. 7 is a line graph displaying the unexposed surface temperature (Y-axis) over time (X-axis) for wallboards of Example 3 during a small-scale fire test in accordance with embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention are premised, at least in part, on the surprising and unexpected discovery that a wallboard comprising a greater number of water voids and a reduced number of foam voids has greater fire endurance. It was discovered that the size of the voids located in the gypsum matrix has significant implications on fire endurance of the wallboard. Specifically, it was found that microscopic, uniformly distributed water voids are generally preferable to large, interconnected foam voids. To prepare a board comprising an increased number of water voids, the water-to-stucco ratio can be increased. In general, the gypsum wallboard comprises a core comprising an interlocking matrix of set gypsum formed from a slurry having a water-to-stucco ratio from about 0.7 to about 2.0.

In general, when a gypsum wallboard is under thermal stress, thermal energy is initially directed to the evaporation of the calcium sulfate-bound water molecules. It is those two molecules of water that render gypsum highly resistant against heat. Upon reaching 215° F., water molecules are driven off, which leads to the formation of calcium sulfate hemihydrates (CaSO₄.½H₂O). When the temperature reaches 250° F., the remaining water is lost as gypsum is converted into calcium sulfate anhydrite. Both reactions are endothermic, meaning gypsum will absorb heat as it is “calcined” from dihydrate to anhydrite.

In a wallboard test assembly, heat is transferred from the furnace to the surface of exposed board. As the surface temperature of the exposed wallboard increases, the temperature gradient across the board increases. As heat transfer continues, the surface temperature of the unexposed wallboard increases as crystallized water in the wallboard is driven off.

The fire endurance of a gypsum article is believed to be directly related to the amount of gypsum contained within the article. It is believed that as the amount of gypsum decreases, the fire endurance of the gypsum article decreases because there is less crystallized water to evaporate. A previous approach to fire endurance focused on the formation of a thicker and/or denser gypsum core (i.e., core comprising more gypsum relative). With increased gypsum, the core comprises an increased amount of chemically bound water within the core, which can act as a heat sink, reduce shrinkage, and increase structural stability and strength.

The current trend in the wallboard industry is to develop light weight, low density wallboard. A low basis weight can be achieved by mixing stucco slurry with a predetermined amount of foam based upon the target basis weight of the wallboard. As the board contains less gypsum per unit volume, there is less crystallized water available for fire endurance of the wallboard. In addition, during exposure to a fire, the percent shrinkage can increase as the board density decreases. Both factors make it increasingly difficult to pass a fire test. High thermal expansion additives are often added to the formulation to improve fire endurance. However, the expansion of large quantities of high thermal expansion particles in low weight wallboard can lead to spalling and crumbling.

Gypsum wallboards can comprise voids derived from the (a) packing of gypsum crystals, (b) evaporation of water, and (c) the presence of any foam additive. In order to make a board with constant density, as foam voids increase, the amount of water voids can be reduced by adjusting down the water-to-stucco ratio; as water voids increase, the amount of foam voids can be reduced by adding less foam (see FIG. 1). Without wishing to be bound by theory, when exposed to fire, the water vapor from CaSO₄.2H₂O must travel through the board before being released into the atmosphere. Foam voids can be relatively large and allow water vapor to quickly escape from the gypsum core during a fire. Since water voids are microscopic, the vapor must overcome a higher flow resistance than when traveling through foam voids. As a result, it takes longer for the water vapor to flow through the board, thus, increasing the fire endurance of the wallboard. Thus a wallboard with an increased number of water evaporation voids, e.g., made with a higher water-to-stucco ratio, can have greater fire endurance. However, if the water-to-stucco ratio is too high (and foam amount too low), vapor pressure can build up, leading to collapse of the wallboard. For effective fire endurance, the gypsum wallboard can be prepared with an optimal water-to-stucco ratio and foam content. To create a wallboard with optimal fire endurance and light weight properties, a balance between water content and fire endurance properties can be achieved.

The water-to-stucco ratio is an important parameter in gypsum board manufacture, as would be understood and appreciated by those of ordinary skill in the art. The water-to-stucco ratio expresses the amount of water per amount of stucco. Manufacturers typically limit the amount of water in a stucco slurry due to the high cost of the fuels used in the heating process during the final drying step to drive off the excess water. High water-to-stucco ratios also lead to an increase in slurry fluidity, which can render the stucco gypsum slurry more difficult to manipulate. Unlike slurries having a high water-to-stucco ratio, slurries having a low water content have an increased rate of gypsum crystal growth during setting because available nucleating sites are concentrated into a smaller volume of the mix. In this scenario, crystal growth is faster and the degree of interlocking of the gypsum crystals is greater. Due to this phenomenon, it is believed that slurries with lower water-to-stucco ratios yield gypsum product of higher strength.

Surprisingly and unexpectedly, it has been discovered that a gypsum board, can have greater fire endurance, even in the absence of additives, than a board with less gypsum. Specifically, a board of lower weight comprising a core with a higher water-to-stucco ratio can have greater fire endurance than a board with a larger gypsum content (e.g., see Table 1, samples 1 and 2). It has been discovered that a wallboard prepared from a slurry comprising a water-to-stucco ratio of about 0.7 to about 2.0 has high fire endurance. The water-to-stucco ratio is calculated based on the weight of water compared to the weight of the dry calcined gypsum. The wallboards of the present invention can have a fire endurance greater than boards prepared with water-to-stucco ratios lower than about 0.7 and of comparable or equivalent board density and thickness. In some embodiments, the water-to-stucco ratio is from about 0.9 to about 1.4. It was discovered that the fire endurance index values level off after a water-to-stucco ratio of 1.4. Increasing the water-to-stucco ratio from 1.2 and 1.4 leads to a 2.7 minute increase in the fire endurance index, while increasing the water-to-stucco ratio from 1.4 to 1.6 leads to a 0.8 minute increase. Therefore, a preferred water-to-stucco ratio is below about 1.4, with the highest cost benefit obtained when the water-to-stucco ratio is from about 1.2 to about 1.4.

In embodiments of the invention, the water-to-stucco ratio can be, e.g., as listed in Tables 1A and 1B below. In the tables, an “X” represents the range “from about [corresponding value in top row] to about [corresponding value in left-most column].” The indicated values represent the water-to-stucco ratio. For ease of presentation, it will be understood that each value represents “about” that value. For example, the first “X” in Table 1A is the range “about 0.7 to about 0.8.” The ranges of the table are between and including the starting and endpoints.

TABLE 1A Starting Point for Water-to-Stucco Ratio Range 0.7 0.8 0.85 0.9 0.95 1.00 1.05 1.10 1.15 1.20 1.25 1.30 1.35 End Point for 0.8 X Water-to-Stucco 0.85 X X Ratio Range 0.9 X X X 0.95 X X X X 1.00 X X X X X 1.05 X X X X X X 1.10 X X X X X X X 1.15 X X X X X X X X 1.20 X X X X X X X X X 1.25 X X X X X X X X X X 1.30 X X X X X X X X X X X 1.35 X X X X X X X X X X X X 1.40 X X X X X X X X X X X X X 1.45 X X X X X X X X X X X X X 1.50 X X X X X X X X X X X X X 1.55 X X X X X X X X X X X X X 1.60 X X X X X X X X X X X X X 1.65 X X X X X X X X X X X X X 1.70 X X X X X X X X X X X X X 1.75 X X X X X X X X X X X X X 1.80 X X X X X X X X X X X X X 1.85 X X X X X X X X X X X X X 1.90 X X X X X X X X X X X X X 1.95 X X X X X X X X X X X X X 2.00 X X X X X X X X X X X X X

TABLE 1B Starting Point for Water-to-Stucco Ratio Range 1.40 1.45 1.50 1.55 1.60 1.65 1.70 1.75 1.80 1.85 1.90 1.95 End Point for 1.45 X Water-to-Stucco 1.50 X X Ratio Range 1.55 X X X 1.60 X X X X 1.65 X X X X X 1.70 X X X X X X 1.75 X X X X X X X 1.80 X X X X X X X X 1.85 X X X X X X X X X 1.90 X X X X X X X X X X 1.95 X X X X X X X X X X X 2.00 X X X X X X X X X X X X

As stated above, an increase in the water-to-stucco ratio leads to an increase in the fluidity of the stucco slurry. Dispersants are generally used in the art to help fluidize the mixture of water and calcium sulfate hemihydrate so that less water is needed to make a flowable slurry. Furthermore, dispersants are added to slurries to reduce production cost by reducing the amount of water that must be removed during the drying step.

Without wishing to be bound by theory, some embodiments may not require a dispersant because slurries having a high water-to-stucco ratio can have sufficient fluidity. In other embodiments, a reduced amount of dispersant may be added to the slurry to impart sufficient fluidity. The stucco slurry generally comprises a dispersant in an amount less than about 0.4% by weight based on the weight of stucco. The amount of dispersant added to the stucco slurry can be an amount less than about 0.1% by weight based on the weight of stucco. In embodiments of the invention, the amount of dispersant by weight based on the weight of stucco can be, e.g., as listed in Table 1C. In the table, an “X” represents the range “from about [corresponding value in top row] to about [corresponding value in left-most column].” The indicated values represent the amount of dispersant (Table 1C). For ease of presentation, it will be understood that each value represents “about” that value. For example, the first “X” in Table 1C is the range “from about 0% to about 0.05%.” The ranges of the table are between and including the starting and endpoints.

TABLE 1C Starting Point for Dispersant Range (%) 0 0.05 0.075 0.1 0.125 0.15 0.175 0.2 0.225 0.25 0.275 0.3 0.325 0.35 0.375 End Point for 0.05 X Dispersant 0.075 X X Range (%) 0.1 X X X 0.125 X X X X 0.15 X X X X X 0.175 X X X X X X 0.2 X X X X X X X 0.225 X X X X X X X X 0.25 X X X X X X X X X 0.275 X X X X X X X X X X 0.3 X X X X X X X X X X X 0.325 X X X X X X X X X X X X 0.35 X X X X X X X X X X X X X 0.375 X X X X X X X X X X X X X X 0.4 X X X X X X X X X X X X X X X

In some embodiments, such dispersants can include naphthalenesulfonates, such as polynaphthalenesulfonic acid and its salts (polynaphthalenesulfonates) and derivatives, which are condensation products of naphthalenesulfonic acids and formaldehyde. Such polynaphthalenesulfonates include sodium and calcium naphthalenesulfonate. The average molecular weight of the naphthalenesulfonates can range from about 3,000 to 27,000, although the molecular weight can be about 8,000 to 10,000. At a given solids percentage aqueous solution, a higher molecular weight dispersant has a higher viscosity, and generates a higher water demand in the formulation, than a lower molecular weight dispersant.

Naphthalenesulfonates include DILOFLO, available from GEO Specialty Chemicals, Cleveland, Ohio; DAXAD, available from Hampshire Chemical Corp., Lexington, Mass.; and LOMAR D, available from GEO Specialty Chemicals, Lafayette, Ind. The naphthalenesulfonates can be used as aqueous solutions in the range of about 35% to about 55% by weight solids content, for example. The naphthalenesulfonates in the form of an aqueous solution, for example, in the range of about 40% to about 45% by weight solids content. The naphthalenesulfonates can be used in dry solid or powder form, such as LOMAR D, for example.

In other embodiments, dispersants known to those skilled in the art useful for improving fluidity in gypsum slurries may be used employed, such as polycarboxylate dispersants. A number of polycarboxylate dispersants, particularly polycarboxylic ethers, are known types of dispersants. One class of dispersants includes two repeating units and is described further in U.S. Pat. No. 7,767,019, which is incorporated herein by reference with regard to dispersants. Examples of these dispersants are products of BASF Construction Polymers, GmbH (Trostberg, Germany) and supplied by BASF Construction Polymers, Inc. (Kennesaw, Ga.) (hereafter “BASF”) and are hereafter referenced as the “PCE211-Type Dispersants.” A particular dispersant of the PCE211-Type Dispersants is designated PCE211 (hereafter “211”). Other polymers in this series include PCE111. PCE211-Type dispersants are described more fully in U.S. Pub. No. US 2007/0255032A1., which is incorporated herein by reference with regard to dispersants. The molecular weight of one type of such PCE211 Type dispersants may be from about 20,000 to about 60,000 Daltons. It has been found that the lower molecular weight dispersants cause less retardation of set time than dispersants having a molecular weight greater than 60,000 Daltons. Generally longer side chain length, which results in an increase in overall molecular weight, provides better dispensability. However, tests with gypsum indicate that efficacy of the dispersant can be reduced at molecular weights above 50,000 Daltons.

Another class of polycarboxylate compounds includes those disclosed in U.S. Pat. No. 6,777,517, which is incorporated herein by reference with regard to dispersants, and hereafter referenced as the “2641-Type Dispersant.” Examples of PCE211-Type and 2641-Type dispersants are manufactured by BASF. Preferred 2641-Type Dispersants are sold by BASF as MELFLUX 2641F, MELFLUX 2651F and MELFLUX 2500L dispersants.

Yet another dispersant family is sold by BASF and referenced as “1641-Type Dispersants.” The 1641-Type dispersant is more fully described in U.S. Pat. No. 5,798,425, which is incorporated herein by reference with regard to dispersants. One of such 1641-Type Dispersants is marketed as MELFLUX 1641F dispersant by BASF. Other dispersants include other polycarboxylate ethers such as COATEX Ethacryl M, available from Coatex, Inc. of Chester, S.C., and lignosulfonates, or sulfonated lignin. Lignosulfonates are water-soluble anionic polyelectrolyte polymers, byproducts from the production of wood pulp using sulfite pulping. One example of a lignin useful in the practice of principles of the present invention is Marasperse C-21 available from Reed Lignin Inc., Greenwich, Conn.

In other embodiments, the composition, wallboard, or method can be “substantially free” of dispersant, which means that the composition, wallboard, or method contains either (i) 0 wt. % based on the weight of stucco, or no such dispersant, or (ii) an ineffective or (iii) an immaterial amount of dispersant. An example of an ineffective amount is an amount below the threshold amount to achieve the intended purpose of using dispersant as one of ordinary skill in the art will appreciate. An immaterial amount may be, e.g., below about 5 wt. %, such as below about 2 wt. %, below about 1 wt. %, below about 0.5 wt. %, below about 0.2 wt. %, below about 0.1 wt. %, or below about 0.01 wt. % based on the weight of stucco as one of ordinary skill in the art will appreciate. However, if desired in alternative embodiments, such ingredients can be included in the composition, wallboard, or method.

Starch can be added to a gypsum composition to improve board strength and paper to core adhesion. Without wishing to be bound by theory, gelatinized starch can be added to the stucco slurry to decrease the fluidity of the slurry. The starch of the present invention can be gelatinized prior to addition to the stucco composition (i.e., pregelatinized). In some embodiments, the gelatinized starch is partially gelatinized when added to the slurry, with remaining gelatinization taking place in the drying step (e.g., in a kiln).

The stucco slurry can comprise gelatinized starch in any amount. In some embodiments, the amount of starch is greater than about 1% by weight based on the weight of stucco. In embodiments of the invention, the amount of gelatinized starch by weight based on the weight of stucco can be, e.g., as listed in Table 1D. In the table, an “X” represents the range “from about [corresponding value in top row] to about [corresponding value in left-most column].” The indicated values represent the amount of gelatinized starch (Table 1D). For ease of presentation, it will be understood that each value represents “about” that value. For example, the first “X” in Table 1D is the range “from about 1% to about 1.5%.” The ranges of the table are between and including the starting and endpoints.

TABLE 1D Start Point for Gelatinized Starch Range (%) 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 End Point for 1.5 X Gelatinized Starch 2 X X Range (%) 2.5 X X X 3 X X X X 3.5 X X X X X 4 X X X X X X 4.5 X X X X X X X 5 X X X X X X X X 5.5 X X X X X X X X X 6 X X X X X X X X X X 6.5 X X X X X X X X X X X 7 X X X X X X X X X X X X 7.5 X X X X X X X X X X X X X 8 X X X X X X X X X X X X X X 8.5 X X X X X X X X X X X X X X X 9 X X X X X X X X X X X X X X X X 9.5 X X X X X X X X X X X X X X X X X 10 X X X X X X X X X X X X X X X X X X

One of ordinary skill in the art will appreciate methods of pregelatinizing raw starch, such as, for example, cooking raw starch in water at temperatures of at least about 185° F. (85° C.), or other methods. Suitable examples of pregelatinized starch include, but are not limited to, PCF 1000 starch, commercially available from Bunge Milling Inc. and AMERIKOR 818 and HQM PREGEL starches, both commercially available from Archer Daniels Midland Company. In addition, the core can optionally comprise a pregelatinized starch characterized as having a “mid-range” viscosity (i.e., having a viscosity from about 20 centipose to about 700 centipose).

Thickeners can be used in some embodiments to acquire the proper rheology for making boards on a forming line. Any thickener required to sufficiently decrease the fluidity of the stucco slurry can be added to the slurry. For example, silica fume, Portland cement, fly ash, clay, cellulosic fiber, and a mixture thereof can be added to the gypsum composition. This is most advantageous for thickening slurries on a line with a line speed greater than 200 ft/minute. High molecular weight polymers, such as polyacrylamide, can also be added to the gypsum slurry to decrease the fluidity of the slurry. In some embodiments, a thickener or mixture of thickeners may be added to the slurry in less than about 10% by weight based on the weight of the stucco.

In some embodiments, high expansion particles can be added to the core. For example, unexpanded vermiculite can be added to the slurry to further improve fire endurance. A gypsum core made from a stucco slurry having an increased water-to-stucco ratio can have a smaller amount of vermiculite to increase fire endurance, as compared to a core prepared with a larger amount of vermiculite and a slurry comprising a low water-to-stucco ratio.

In some embodiments, the stucco slurry comprises less than about 5% of vermiculite by weight. Relatively low expansion vermiculite, such as that referred to as “Grade No. 5” unexpanded vermiculite (with a typical particle size of less than about 0.0157 inches (0.40 mm)), or high expansion particulates in the form of vermiculite with a high volume of expansion relative to Grade No. 5 vermiculite (U.S. grading system), and other low expansion vermiculites may be utilized. In other embodiments, high expansion vermiculites can be used that are classified under different grading systems. Such high expansion vermiculites should have substantially similar expansion and/or thermal resistance characteristics typical of those discussed herein. For example, in some embodiments, a vermiculite classified as European, South American, or South African Grade 0 (micron) or Grade 1 (superfine) can be used.

In some embodiments, the high expansion vermiculite used can include commercial U.S. grade 4 vermiculite commercially-available through a variety of sources. Commercial producers can provide specifications for physical properties of the high expansion vermiculite, such as Mohs hardness, total moisture, free moisture, bulk density, specific ratio, aspect ratio, cation exchange capacity, solubility, pH (in distilled water), expansion ratio, expansion temperature, and melting point, for example. It is contemplated that in different embodiments using different sources of high expansion vermiculites, these physical properties will vary.

In some embodiments, the high expansion vermiculite particles are generally distributed throughout the core portion of the gypsum panels. In other embodiments, the high expansion vermiculite particles are generally evenly distributed throughout the core portion of the gypsum panels. The high expansion vermiculite can be generally randomly distributed throughout any reduced density portions of the core. In some embodiments, it may be desirable to have a different vermiculite distribution in denser portions of a board, such as in any increased density gypsum layer adjacent the panel face(s) or in portions of the core with greater density along the panel edges. In other embodiments, the high expansion vermiculite may be substantially excluded from those denser portions of the panels, such as hardened edges and faces of the panels. Such variations in vermiculite particle contents and distribution in the denser portions of the panels may be as a result of drawing core slurry from the core slurry mixer for use in those portions of the panel, by introduction of the vermiculite through other appropriate means into the slurry for the reduced density core portions of the panel, by using edge mixers, or other means known to those skilled in the art.

In other embodiments, the composition, wallboard, or method can be “substantially free” of high expansion materials such as vermiculite, which means that the composition, wallboard, or method contains either (i) 0 wt. % based on the weight of stucco, or no such high expansion materials such as vermiculite, or (ii) an ineffective or (iii) an immaterial amount of high expansion material such as vermiculite. An example of an ineffective amount is an amount below the threshold amount to achieve the intended purpose of using high expansion materials such vermiculite as one of ordinary skill in the art will appreciate. An amount may be, e.g., below about 5 wt. %, such as below about 2 wt. %, below about 1 wt. %, below about 0.5 wt. %, below about 0.2 wt. %, below about 0.1 wt. %, or below about 0.01 wt. % based on the weight of stucco as one of ordinary skill in the art will appreciate. However, if desired in alternative embodiments, such ingredients can be included in the composition, wallboard, or method.

The present invention can be practiced employing compositions and methods similar to those employed in the art to prepare various set gypsum-containing products. In the core, the stucco (or calcined gypsum) component used to form the crystalline matrix typically comprises, consists essentially of, or consists of beta calcium sulfate hemihydrate, water-soluble calcium sulfate anhydrite, alpha calcium sulfate hemihydrate, or mixtures of any or all of these, from natural or synthetic sources. In some embodiments, the stucco may include non-gypsum minerals, such as minor amounts of clays or other components that are associated with the gypsum source or are added during the calcination, processing and/or delivery.

The gypsum core may comprise conventional additives in the practice of the invention in customary amounts to impart desirable properties and to facilitate manufacturing, such as, for example, suitable aqueous foam, set accelerators, set retarders, recalcination inhibitors, binders, adhesives, leveling or nonleveling agents, bactericides, fungicides, pH adjusters, colorants, reinforcing materials, fire retardants, water repellants, fillers, dimensional strengtheners, and mixtures thereof. In addition, the gypsum core can comprise additives such as phosphonic and/or phosphonate compounds, phosphoric and/or phosphate compounds, carboxylic and/or carboxylate compounds, boric and/or borate compounds, and mixtures thereof.

Accelerators can be used in the gypsum-containing compositions of the present invention, as described in U.S. Pat. No. 6,409,825, herein incorporated by reference with regard to accelerators. One desirable heat resistant accelerator (HRA) can be made from the dry grinding of landplaster (calcium sulfate dihydrate). Small amounts of additives (normally about 5% by weight) such as sugar, dextrose, boric acid, and starch can be used to make this HRA. Sugar, or dextrose, is currently preferred. Another useful accelerator is “climate stabilized accelerator” or “climate stable accelerator,” (CSA) as described in U.S. Pat. No. 3,573,947, herein incorporated by reference with regard to accelerators.

In some embodiments, a trimetaphosphate compound is added to the gypsum slurry used to make the core to enhance the strength of the board and to reduce the permanent deformation of the gypsum product. Gypsum compositions including trimetaphosphate compounds are disclosed in U.S. Pat. No. 6,342,284, herein incorporated by reference with regard to trimetaphosphate compounds. Exemplary trimetaphosphate salts include sodium, potassium or lithium salts of trimetaphosphate, such as those available from Astaris, LLC., St. Louis, Mo.

In embodiments of the invention, a foaming agent can be employed to yield voids, e.g., small air voids, in the set gypsum products. Foam may be introduced into the stucco gypsum slurry by foam pump. Alternately, liquid soap may be directly added to the stucco gypsum slurry. Many such foaming agents are well known and readily available commercially, e.g., from GEO Specialty Chemicals in Ambler, Pa. For further descriptions of useful foaming agents, see, for example: U.S. Pat. Nos. 4,676,835, 5,158,612, 5,240,639, and 5,643,510, which are, with regard to foaming agents, hereby incorporated by reference.

In many cases it will be preferred to form air voids in the gypsum product, in order to help maintain its strength. This can be accomplished by employing a foaming agent that generates foam that is relatively unstable when in contact with calcined gypsum slurry. Preferably, this is accomplished by blending a major amount of foaming agent known to generate relatively unstable foam, with a minor amount of foaming agent known to generate relatively stable foam.

Such a foaming agent mixture can be pre-blended “off-line”, i.e., separate from the process of preparing foamed gypsum product. However, it is preferable to blend such foaming agents concurrently and continuously, as an integral “on-line” part of the process. This can be accomplished, for example, by pumping separate streams of the different foaming agents and bringing the streams together at, or just prior to, the foam generator that is employed to generate the stream of aqueous foam which is then inserted into and mixed with the calcined gypsum slurry. By blending in this manner, the ratio of foaming agents in the blend can be simply and efficiently adjusted (for example, by changing the flow rate of one or both of the separate streams) to achieve the desired void characteristics in the foamed set gypsum product. Such adjustment will be made in response to an examination of the final product to determine whether such adjustment is needed. Further description of such “on-line” blending and adjusting can be found in U.S. Pat. No. 5,643,510, and in U.S. Pat. No. 5,683,635, which is hereby incorporated by reference with regard to foaming agents.

An example of one type of foaming agent, useful to generate unstable foams, has the formula

ROSO₃⊖M⊕  (Q)

wherein R is an alkyl group containing from 2 to 20 carbon atoms, and M is a cation. Preferably, R is an alkyl group containing from 8 to 12 carbon atoms.

An example of one type of foaming agent, useful to generate stable foams, has the formula

CH₃(CH₂)_(x)CH₂(OCH₂CH₂)_(y)OSO₃⊖M⊕  (J)

wherein X is a number from 2 to 20, Y is a number from 0 to 10 and is greater than 0 in at least 50 weight percent of the foaming agent, and M is a cation.

In some preferred embodiments of the invention, foaming agents having the formulas (Q) and (J) above are blended together, such that the formula (Q) foaming agent and the portion of the formula (J) foaming agent wherein Y is 0, together constitute from 86 to 99 weight percent of the resultant blend of foaming agents.

In some preferred embodiments of the invention, the aqueous foam has been generated from a pre-blended foaming agent having the formula

CH₃(CH₂)_(x)CH₂(OCH₂CH₂)_(y)OSO₃⊖M⊕  (Z)

wherein X is a number from 2 to 20, Y is a number from 0 to 10 and is 0 in at least 50 weight percent of the foaming agent, and M is a cation. Preferably, Y is 0 in from 86 to 99 weight percent of the formula (Z) foaming agent.

Foam can be introduced into the core slurry in amounts that provide a reduced core density and panel weight. The introduction of foam in the core slurry in the proper amounts, formulations and processes can produce a desired network and distribution of air voids, and walls between the air voids, within the core of the final dried panels. In some embodiments, the air void sizes, distributions and/or wall thickness between air voids provided by the foam composition and foam introduction system are in accordance with those discussed below, as well as those that provide comparable density, strength and related properties to the panels. This air void structure permits the reduction of the gypsum and other core constituents and the core density and weight, while substantially maintaining (or in some instances improving) the panel strength properties, such as core compressive strength, and the panel rigidity, flexural strength, nail pull resistance, among others.

In some such embodiments, the mean equivalent sphere diameter of the air voids can be at least about 75 μm, and in other embodiments at least about 100 μm. In other embodiments, the mean equivalent sphere diameter of the air voids can be from about 75 μm to about 400 μm. In yet other embodiments, the mean equivalent sphere diameter of the air voids can be from about 100 μm to about 350 μm with a standard deviation from about 100 to about 225. In other embodiments, the mean equivalent sphere diameter of the air voids may be from about 125 μm to about 325 μm with a standard deviation from about 100 to about 200.

In some embodiments, from about 15% to about 70% of the air voids have an equivalent sphere diameter of about 150 μm or less. In other embodiments, from about 45% to about 95% of the air voids have an equivalent sphere diameter of about 300 μm or less, and from about 5% to about 55% of the air voids have an equivalent sphere diameter of about 300 μm or more. In other embodiments, from about 45% to about 95% of the air voids have an equivalent sphere diameter of about 300 μm or less, and from about 5% to about 55% of the air voids have an equivalent sphere diameter from about 300 μm to about 600 μm. In the discussion of average air void sizes herein, voids in the gypsum core that are about 5 μm or less are not considered when calculating the number of air voids or the average air void size.

In those and other embodiments, the thickness, distribution and arrangement of the walls between the voids in such embodiments, alone and/or in combination with a desired air void size distribution and arrangement, also permit a reduction in the panel core density and weight, while substantially maintaining (or in some instances improving) the panel strength properties. In some such embodiments, the average thickness of the walls separating the air voids may be at least about 25 μm. In some embodiments, the walls defining and separating air voids within the gypsum core may have an average thickness from about 25 μm to about 200 μm, from about 25 μm to about μm in other embodiments, and from about 25 μm to about 50 μm in still other embodiments. In yet other embodiments, the walls defining and separating air voids within the gypsum core may have an average thickness from about 25 μM to about 75 μm with a standard deviation from about 5 to about 40. In yet other embodiments, the walls defining and separating air voids within the gypsum core may have an average thickness from about 25 μM to about 50 μm with a standard deviation from about 10 to about 25.

Examples of the use of foaming agents to produce desired void and wall structures include those discussed in U.S. Pat. No. 5,643,510 and US Patent Appl. No. 2007/0048490, which are hereby incorporated by reference with respect to foaming agents, voids, and wall structures. In some embodiments, a combination of a first more stable foaming agent and a second less stable foaming agent can be used in the core slurry mixture. In other embodiments, only one type of foaming agent is used, so long as the desired density and panel strength requirements are satisfied. The approaches for adding foam to a core slurry are known in the art and examples of such an approach is discussed in U.S. Pat. Nos. 5,643,510 and 5,683,635, the disclosures of which are, with regard to foaming agents, hereby incorporated by reference.

The foaming agent can be added to the slurry in any sufficient amount. In some embodiments, to the slurry is added foaming agent effective to form a board having active foaming agent in an amount from about 0.1 lb to about 2 lb per 1000 ft² of board. In some embodiments, to the slurry is added foaming agent effective to form a board having active foaming agent in an amount from about 0.1 lb to about 2 lb per 1000 ft² of board. In embodiments of the invention, the active foaming agent in the board can be, e.g., as listed in Table 1E. In the table, an “X” represents the range “from about [corresponding value in top row] to about [corresponding value in left-most column].” The indicated values represent the foaming agent in lb/1000 ft² (Table 1E). For ease of presentation, it will be understood that each value represents “about” that value. For example, the first “X” in Table 1E is the range “from about 0.1 lbs/ft³ to about 0.2 lbs/ft³.” The ranges of the table are between and including the starting and endpoints.

TABLE 1E Starting Point for Foaming Agent Range (lb/1000 ft²) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 End Point for 0.2 X Foaming Agent 0.3 X X Range (lb/1000 ft²) 0.4 X X X 0.5 X X X X 0.6 X X X X X 0.7 X X X X X X 0.8 X X X X X X X 0.9 X X X X X X X X 1 X X X X X X X X X 1.1 X X X X X X X X X X 1.2 X X X X X X X X X X X 1.3 X X X X X X X X X X X X 1.4 X X X X X X X X X X X X X 1.5 X X X X X X X X X X X X X X 1.6 X X X X X X X X X X X X X X X 1.7 X X X X X X X X X X X X X X X X 1.8 X X X X X X X X X X X X X X X X X 1.9 X X X X X X X X X X X X X X X X X X 2 X X X X X X X X X X X X X X X X X X X

In other embodiments, the composition, wallboard, or method can be “substantially free” of foaming agent, which means that the composition, wallboard, or method contains either (i) 0 wt. % based on the weight of stucco, or no such foaming agent, or (ii) an ineffective or (iii) an immaterial amount of foaming agent. An example of an ineffective amount is an amount below the threshold amount to achieve the intended purpose of using foaming agent as one of ordinary skill in the art will appreciate. An amount may be, e.g., below about 5 wt. %, such as below about 2 wt. %, below about 1 wt. %, below about 0.5 wt. %, below about 0.2 wt. %, below about 0.1 wt. %, or below about 0.01 wt. % based on the weight of stucco as one of ordinary skill in the art will appreciate. However, if desired in alternative embodiments, such ingredients can be included in the composition, wallboard, or method.

To prepare a board, a mixture of at least stucco and water in slurry form can be deposited on a sheet and formed into a layer to create a board, in a fashion similar to the manufacturing of preforms on an industrial scale. The slurry can be prepared using a water-to-stucco ratio in the range from about 0.7 to about 2.0. The slurry can be spread across the width of the first sheet at a predetermined approximate thickness to form the core. In an industrial setting, the continuous panel is transported along a conveyor to permit time for gypsum hydration. When the core is sufficiently hydrated and hardened, it is cut into one or more desired sizes to form individual gypsum boards. The boards are then transferred into and passed through a kiln at temperatures sufficient to dry the panels to a desired moisture level. In some embodiments, the cover sheets are bonded to the set gypsum core by a top and bottom high density bonding layer.

The wallboard of the present invention can have a board density of about 24 lbs/ft³ to about 48 lbs/ft³. In some embodiments, the board density is from about 24 lbs/ft³ to about 40 lbs/ft³. In some embodiments, the board density is from 24 lbs/ft³ to about 33 lbs/ft³. In embodiments of the invention, the board density can be, e.g., as listed in Table 1F. In the table, an “X” represents the range “from about [corresponding value in top row] to about [corresponding value in left-most column].” The indicated values represent the board density in lbs/ft³ (Table 1F). For ease of presentation, it will be understood that each value represents “about” that value. For example, the first “X” in Table 1F is the range “from about 24 lbs/ft³ to about 25 lbs/ft³.” The ranges of the table are between and including the starting and endpoints.

TABLE 1F Starting Point for Board Density (lbs/ft³) 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 End Point for 25 X Board Density 26 X X (lbs/ft³) 27 X X X 28 X X X X 29 X X X X X 30 X X X X X X 31 X X X X X X X 32 X X X X X X X X 33 X X X X X X X X X 34 X X X X X X X X X X 35 X X X X X X X X X X X 36 X X X X X X X X X X X X 37 X X X X X X X X X X X X X 38 X X X X X X X X X X X X X X 39 X X X X X X X X X X X X X X X 40 X X X X X X X X X X X X X X X X

The typical thickness of gypsum boards is ½ inch and ⅝inch, but may range from ¼ inch to 1 inch. A wallboard of any thickness can be produced using the presently described methods and systems. In embodiments of the invention, the wallboard thickness can be, e.g., as listed in Table 1G. In the table, an “X” represents the range “from about [corresponding value in top row] to about [corresponding value in left-most column].” The indicated values represent the thickness of a board in inches (Table 1G). For ease of presentation, it will be understood that each value represents “about” that value. For example, the first “X” in Table 1G is the range “from about 0.59 inches to about 0.6 inches.” The ranges of the table are between and including the starting and endpoints.

TABLE 1G Starting Point for Wallboard Thickness (inches) 0.59 0.6 0.61 0.62 0.63 0.64 End Point for Wallboard 0.6 X Thickness (inches) 0.61 X X 0.62 X X X 0.63 X X X X 0.64 X X X X X 0.65 X X X X X X

Paper sheets, such as Manila paper or kraft paper, can be used as the cover sheets. Useful cover sheet paper includes Manila 7-ply and News-Line 5-ply, available from United States Gypsum Corporation, Chicago, Ill.; Grey-Back 3-ply and Manila Ivory 3-ply, available from Caraustar, Newport, Ind.; and Manila heavy paper and MH Manila HT (high tensile) paper, available from United States Gypsum Corporation, Chicago, Ill. An exemplary back cover sheet paper is 5-ply newsline. In addition, the cellulosic paper can comprise any other material or combination of materials. For example, the cover sheets may comprise glass fibers, ceramic fibers, mineral wool, or a combination of the aforementioned materials.

In other embodiments, the cover sheet can comprise, consist essentially of, or consist of a mat, such as an unwoven fiberglass mat, sheet materials of other fibrous or non-fibrous materials, or combinations of paper and other fibrous materials maybe used as one or both of the cover sheets. As used herein, the term “mat” includes mesh materials. Fibrous mats can include any suitable fibrous mat material. For example, in some embodiments, the cover sheet can be a mat made from glass fiber, polymer fiber, mineral fiber, organic fiber, or the like or combinations thereof. Polymer fibers include, but are not limited to, polyamide fibers, polyaramide fibers, polypropylene fibers, polyester fibers (e.g., polyethylene teraphthalate (PET)), polyvinyl alcohol (PVOH), and polyvinyl acetate (PVAc). Examples of organic fibers include cotton, rayon, and the like. The fibers of the mat can be coated or uncoated. Selecting a suitable type of fibrous mat will depend, in part, on the type of application in which the board is used.

In some embodiments, the boards of the present invention have a density less than 40 lb/ft³ and nail pull resistance that can meet the standard of ASTM C473-09 (e.g., ASTM C473-09, method B). More particularly, such boards, when having a thickness of about % inch, can have a nail-pull resistance of at least about 70 lbs as determined according to the standard of ASTM C473-09 (e.g., ASTM C473-09, method B). In embodiments of the invention, the nail pull resistance can be, e.g., as listed in Table 1H. In the table, an “X” represents the range “from about [corresponding value in top row] to about [corresponding value in left-most column].” The indicated values represent the nail pull resistance of a board in lbs (Table 1H). For ease of presentation, it will be understood that each value represents “about” that value. For example, the first “X” in Table 1H is the range “from about 70 lbs to about 72 lbs.” The ranges of the table are between and including the starting and endpoints.

TABLE 1H Starting Point for Nail Pull Resistance (lbs) 70 72 74 76 78 80 82 84 86 88 90 92 94 End Point for Nail 72 X Pull Resistance (lbs) 74 X X 76 X X X 78 X X X X 80 X X X X X 82 X X X X X X 84 X X X X X X X 86 X X X X X X X X 88 X X X X X X X X X 90 X X X X X X X X X X 92 X X X X X X X X X X X 94 X X X X X X X X X X X X 96 X X X X X X X X X X X X X

In some embodiments, assemblies can be constructed, using gypsum boards formed according to principles of the present invention, that conform to the specification of Underwriters Laboratories, Inc. (UL®) assemblies, such as U419, U305, and U423. The face of one side of the assembly can be exposed to increasing temperatures for a period of time in accordance with a heating curve, such as those discussed in the ASTM E119 (e.g., ASTM E119-09a) procedures. The temperatures proximate the heated side and the temperatures at the surface of the unheated side of the assembly are monitored during the tests to evaluate the temperatures experienced by the exposed gypsum panels and the heat transmitted through the assembly to the unexposed panels. One useful indicator of the fire performance of gypsum panels in assemblies, for example those utilizing loaded, wood stud frames as called for in the ASTM E119 fire tests, is discussed in the article Shipp, P. H., and Yu, Q., “Thermophysical Characterization of Type X Special Fire Resistant Gypsum Board,” Proceedings of the Fire and Materials 2011 Conference, San Francisco, 31 Jan.-2 Feb. 2011, Interscience Communications Ltd., London, UK, pp. 417-426. The article discusses an extensive series of E119 fire tests of load bearing wood framed wall assemblies and their expected performance under the E119 fire test procedures. U.S. Pat. No. 8,323,785 is incorporated by reference herein with regard to ASTM E119.

In some embodiments, an assembly of gypsum boards formed according to principles of the present invention and in accordance with the specification of a U419 assembly, with or without cavity insulation, has a fire rating of at least about 60 minutes. In some embodiments, an assembly of gypsum boards formed according to principles of the present invention and in accordance with the specification of a U305 assembly has a fire rating of at least about 55 minutes. In some embodiments, an assembly of gypsum boards formed according to principles of the present invention and in accordance with the specification of a U305 assembly has a fire rating of at least about 60 minutes. In some embodiments, an assembly of gypsum boards formed according to principles of the present invention and in accordance with the specification of a U423 assembly has a fire rating of at least about 60 minutes.

In addition to common testing methods, the utility of the present invention to increase fire endurance can be analyzed using a small-scale fire endurance index (FEI) test. The FEI test is a small scale testing apparatus and method developed as an alternative to typical large scale wallboard testing. Fire endurance ratings are typically obtained by performing a full-size (at 100 ft² of wall area) fire test in a certified fire test laboratory per ASTM standards, which is time-consuming, expensive, and unsuitable for bench-top studies and quality control.

A schematic diagram of a testing system 200 is shown, in cross section, in FIG. 2. The testing system 200 includes a muffle furnace 202 having an enclosure 204 forming a furnace chamber 206. The chamber 206 is closeable with a door 208 and includes a heat source 210 therewithin. The heat source 210 may be any known type of heat source such as a fuel-fired combustor or an electric-resistive heater, which operates to create a generally uniformly distributed temperature profile within the chamber 206.

In the illustration of FIG. 2, a board sample 212 is shown disposed within the furnace chamber 206 during a test. The sample 212 is mounted vertically within the chamber 206 in the illustrated embodiment at an offset distance from a door opening such that a gap 214 is formed between a back face 215 of the sample 212 and an oven-facing side of the door 208. Spacers 216 are disposed at a distance from one another between the sample 212 and the door 208 to simulate studs that space apart wallboards in a finished wall assembly. Although the gap 214 is shown empty, in an alternative embodiment the gap 214 may be filled with a wall-insulation material. Moreover, metal or wooden studs may be used in place of the spacers 216. The spacers may be connected to the sample 212 and, in certain embodiments, may be subjected to a compressive load along with the sample 212 to simulate a load-bearing wall.

A thermocouple 218 or other temperature-sensing device is connected close to the back face 215 of the sample during testing. The back face 215 can be thicker than the front face of the sample. The thermocouple 218 has a sensing tip at a small distance from the surface of the sample 212. In alternative embodiments, the sending tip can touch or be within the sample 212. The thermocouple 218 is configured to sense a surface temperature or a temperature near the surface of the back face of the sample 212 during testing. The thermocouple 218 is connected to a data acquisition unit 220, which operates to provide power to the thermocouple 218, receive information therefrom indicative of the surface temperature of the sample 212, record the temperature information and, optionally or with the aid of a computer (not shown), plot the temperature information over time or otherwise analyze the information numerically.

When a test is conducted, the temperature of the muffle furnace chamber 206 is gradually increased over time by appropriately controlling the intensity of the heat source 210. In one embodiment, a furnace temperature sensor 222 is disposed to measure the temperature of the furnace chamber 206, provide information indicative of the furnace chamber temperature to a heater controller 224 and, optionally, also to the data acquisition unit 220. The heater controller 224 may operate in a closed loop fashion based on the information provided by the sensor 222 to provide a predetermined heating profile for the chamber 206 by appropriately and automatically adjusting the intensity of the heat source 210. The temperature rise of the chamber 206 may also optionally be recorded by the data acquisition unit 220 for establishing testing integrity.

A sample heating profile of the furnace chamber is shown in the time plot of FIG. 3. As can be seen from the plot, where a desired chamber temperature (deg. F) is plotted along the vertical axis and time (min.) is plotted along the horizontal axis, the chamber 206 is heated gradually following a logarithmic trend for about the first 43 minutes of the test from a temperature of about 400° F. to a temperature of about 1,423° F., and is maintained at that temperature for the remainder of the test, which in the illustrated graph continues for about 1 hour. Thus, the test is conducted over a first, heating period 226, and then continues over a stable period 228, as marked on the chart of FIG. 3.

It has been determined that heat transfer through the sample 212 during a test, as gleaned by the measured surface temperature on the back face 215 of the sample, is concomitant to and indicative of the expected heat transfer through a wallboard in a full scale fire test. In essence, the test describes herein determines the rate of heat transfer through the sample. In one embodiment, temperature readings taken on both sides of the board can be used to estimate, in real time, the heat transfer rate through the board. By comparing the heat transfer curves of different products and correlating the curves to their actual fire test results, judgment and prediction of the performance of fire endurance of different products are advantageously enabled. In the test setup shown in FIG. 2, sample dimension was selected to be a rectangular sample having dimensions of 6.125″×6.625″ and a thickness of 0.625″. The depth of the cavity 214 was ⅞″, and the thermocouple 218 was located in the geometrical center of the door 208, where the sensing probe of the thermocouple 218 protruded about 11/16″ from the inside surface of the door 208 in the direction of the sample 212. In this way, the tip of the thermocouple was 3/16″ away from the surface of the sample. A glass wool frame was placed against the sample to act as the spacer 216 and keep the sample in place while also sealing the door frame against heat leakage. For half-inch thick samples, a metal frame of 0.125″ thickness can be placed behind the sample to maintain the gap between the thermocouple and the sample and preserve the remaining test setup. The controller 224 of the muffle furnace was set to run from 200° C. to 773° C. The actual temperature curve of the muffle furnace at the front end is shown in FIG. 3.

The test provides a temperature-time curve for a specific board sample. Fire endurance index (FEI) can be determined from the curve. Fire endurance index is defined as the time required to reach 600° F. at the backside of a test specimen in the small scale fire test. Data points A, B, C, and D are plotted, and the correlation between FEI and fire endurance time from U419 full-size fire test is shown in FIG. 4. Other designs of fire test assembly such as U305 and U423 can be extrapolated from FEI as well.

In some embodiments, the gypsum board has a Fire Endurance Index (FEI) at least 3 minutes greater than a board comprising set gypsum formed with a water-to-stucco ratio of less than about 0.7. In some embodiments, the gypsum board has a Fire Endurance Index (FEI) at least 4 minutes greater than a board comprising set gypsum formed with a water-to-stucco ratio of less than about 0.7.

It shall be noted that the preceding are merely examples of embodiments. Other exemplary embodiments are apparent from the entirety of the description herein. It will also be understood by one of ordinary skill in the art that each of these embodiments may be used in various combinations with the other embodiments provided herein. The following examples further illustrate the invention but, of course, should not be construed as in any way limiting its scope.

Example 1 Effect of Water-to-Stucco Ratio on Fire Endurance

This Example demonstrates the effect of the water-to-stucco ratio (WSR) on the fire endurance of a wallboard. Accordingly, five gypsum boards (samples 1-5) made with water-to-stucco ratios ranging from 1.0 to 1.9 were tested using the FEI small-scale testing device (FIG. 2).

TABLE 2 Additives ADVANTEX ® 790C-16W continuous glass strands (Owens Corning, Toledo, OH) Diloflo Dispersant (Geo Specialty Chemicals, Cleveland, OH) CSA Accelerator, Pre-Mix Southard Pregelatinized Starch, Corn Flour (Yellow) (Bunge Milling, St. Louis, MO) Sodium trimetaphosphate (Innophos, Cranberry, NJ) Hyonic PFM 33 (Stable soap), Hyonic 25-AS (Unstable soap) (Geo Specialty Chemicals, Inc., Cedartown, GA) VERSENEX ™ 80 Chelating Agent Retarder (Dow Chemical, Midland, MI)

In a laboratory, a stucco slurry was prepared by mixing 700 g stucco, 3.5 g of accelerator (finely ground gypsum), 10 g dry pregelatinized starch, 1.4 g sodium trimetaphosphate, and 1 g chopped fiberglass (see Table 2). Predetermined amounts of water corresponding to the amount required to form water-to-stucco ratios of 1.0, 1.2, 1.4, 1.6, and 1.9 were weighed in separate steel bowls. To each steel bowl was added 0.9 g dispersant and up to 2 drops of retarder. After the water solution reached room temperature, the steel bowl was installed under a Hobart mixer. The stucco mixture was added to the water solution and immediately mixed. Subsequently, the foam pump was activated and the foam was injected into the bowl according to a predetermined injection rate. The foam injection time was pre-calculated to make boards having a dry density of approximately 1700 lbs/MSF, with different injection rates required for each board. After foam injection, the composition was mixed for an additional 5 seconds. The slurry was immediately poured into a premade paper envelop (made with 34 lbs/MSF newsline and 49 lbs/MSF manila paper), and cast by sandwiching between two aluminum plates that were spaced to make % inch boards. After casting, the boards were placed into an oven preset at 350° F. After 30 minutes, the boards were transferred to another oven that was preset at 110° F. The boards were left in the oven for two nights, and then removed from the oven and weighed. The dry boards each were cut into samples of 6.625 inches×6.125 inches.

TABLE 3 Fire Endurance of Boards Made With Various Water-to-Stucco Ratios Board Foam Board Basis Injection Fire Weight Thickness Weight Density Rate Endurance Sample WSR (g) (inches) (lbs/MSF) (lbs/ft³) (sec) Index (min) 1 1.0 225.2 0.639 1760 33.1 21 52.0 2 1.2 211.7 0.638 1655 31.1 18 54.4 3 1.4 212.2 0.637 1659 31.3 13 57.1 4 1.6 216 0.627 1688 32.3 7 57.9 5 1.9 219.2 0.636 1713 32.3 0 60.0

Samples 1-5 were individually tested in the small-scale device (FIG. 2) to determine their respective FEI. Temperature traces for each of the five samples are shown in FIG. 5, where time is plotted along the horizontal axis and the unexposed surface temperature of the back-face of each sample is plotted along the vertical axis. In the graph of FIG. 5, line 301 represents the temperature trace for a board made with a WSR of 1.0 (sample 1), line 302 represents the temperature trace for a board made with a WSR of 1.2 (sample 2), line 303 represents the temperature trace for a board made with a WSR of 1.4 (sample 3), line 304 represents the temperature trace for a board made with a WSR of 1.6 (sample 4), line 305 represents the temperature trace for a board made with a WSR of 1.9 (sample 5), and a “FEI” line 306 extends horizontally from a temperature of 315.6° C. (600° F.) to denote the FEI for both samples.

As can be calculated from the graph of FIG. 5, the fire endurance index of the board made with a WSR of 1.0 was 52.0 minutes (sample 1), 54.4 minutes for the board made with a WSR of 1.2 (sample 2), 57.1 minutes for the board made with a WSR of 1.4 (sample 3), 57.9 minutes for the board made with a WSR of 1.6 (sample 4), and 60.0 minutes for the board made with a WSR of 1.9 (sample 5). The heat curves in FIG. 5 suggests that after about 250° F., the temperature at which the boards complete calcination, the heat transfer through the samples depends on the water-to-stucco ratio, and therefore, the number of microscopic water voids. Boards with a high water-to-stucco ratio contain a greater number of microscopic voids, making it more difficult for water vapor to escape the core.

This Example demonstrates that a higher water-to-stucco ratio increases the fire endurance of a gypsum wallboard.

Example 2 The Effect of Board Weight on the Fire Endurance of Board with High Water-to-Stucco Ratio

This Example demonstrates the effect of a high water-to-stucco ratio on the fire endurance of a light weight/low density wallboard. Accordingly, a board with a basis weight of 1235 lbs/MSF (sample 6), a board with a basis weight of 1357 lbs/MSF (sample 7), and a board with a basis weight of 1422 lbs/MSF (sample 8) were tested using FEI small-scale testing device (FIG. 2). Samples 6-8 were made using a water-to-stucco ratio of 1.9.

In a laboratory, a stucco slurry was prepared by mixing 700 g stucco, 3.5 g of accelerator (finely ground gypsum), 10 g dry pregelatinized starch, 1.4 g sodium trimetaphosphate, and 1 g chopped fiberglass (see Table 2). Predetermined amounts of water corresponding to the amount required to form a water-to-stucco ratio of 1.9 were weighed into a Warring blender. To the Warring blender was added 0.9 g dispersant and 0.2 g to 0.6 g of liquid soap. After the water solution reached room temperature, the stucco mixture was added to the blender and immediately mixed. As the high speed mixing action draw air into the slurry, foam was generated. After seven seconds, the slurry was poured into a premade paper envelop (made with 41 lbs/MSF newsline and 53 lbs/MSF manila paper), and cast by sandwiching between two aluminum plates that were spaced to make ⅝inch boards. After casting, the boards were placed into an oven preset at 350° F. After 30 minutes, the boards were transferred to another oven that was preset at 110° F. The boards were left in the oven for two nights, and then removed from the oven and weighed. The dry boards were cut into samples of 6.625 inches×6.125 inches.

TABLE 4 Fire Endurance Index of Low Density Wallboard Board Fire Basis Board Endurance Weight Weight Thickness Density Index Sample (lbs/MSF) WSR (g) (inches) (lbs/ft³) (min) 6 1235 1.9 158.04 0.613 24.2 57.3 7 1357 1.9 173.55 0.609 26.7 59.5 8 1422 1.9 181.91 0.610 27.6 61.3

Samples 6-8 were individually tested in the small-scale device (FIG. 2) to determine their respective FEI. Temperature traces for each of the three samples are shown in FIG. 6, where time is plotted along the horizontal axis and the unexposed surface temperature of the back-face of each sample is plotted along the vertical axis. In FIG. 6, the short-dashed line 307 represents the temperature trace for the board with a basis weight of 1235 lbs/MSF (sample 6), the solid line 308 represents the temperature trace for the board with a basis weight of 1357 lbs/MSF (sample 7), the short-dashed line 309 represents the temperature trace for the board with a basis weight of 1422 lbs/MSF (sample 8), and a “FEI” line 310 extends horizontally from a temperature of 315.6° C. (600° F.) to denote the FEI indexes for both samples.

As can be calculated from the graph of FIG. 6, the FEI was of the board with a basis weight of 1235 lbs/MSF was 57.3 minutes (sample 6), 59.5 minutes for the board with a basis weight of 1357 lbs/MSF (sample 7), and 61.3 minutes for the board with a basis weight of 1422 lbs/MSF (sample 8).

This Example demonstrates that gypsum wallboard of varying weights at about ⅝ inch thickness exhibit fire endurance with a high water-to-stucco ratio.

Example 3 High Water-to-Stucco Ratio and Vermiculite

This Example examines the effect of vermiculite in conjunction with a high water-to-stucco ratio on the fire endurance of wallboard. Accordingly, five gypsum boards (samples 9-13) made with vermiculite amounts ranging from 0 to 100 lbs/MSF were tested using the fire endurance index (FEI) small-scale testing device (FIG. 2). Samples 9-13 were made using a water-to-stucco ratio of 1.4.

TABLE 5 Additives ADVANTEX ® 790C-16W continuous glass strands (Owens Corning, Toledo, OH) Vermiculite Concentrate Grade 4 (Virginia Vermiculite, Louisa, VA) Diloflo Dispersant (Geo Specialty Chemicals, Cleveland, OH) CSA Accelerator, Pre-Mix Southard Pregelatinized Starch, Corn Flour (Yellow) (Bunge Milling, St. Louis, MO) Sodium trimetaphosphate (Innophos, Cranberry, NJ) Hyonic PFM 33 (Stable soap), Hyonic 25-AS (Unstable soap) (Geo Specialty Chemicals, Inc., Cedartown, GA) VERSENEX ™ 80 Chelating Agent Retarder (Dow Chemical, Midland, MI)

In a laboratory, a stucco slurry was prepared by mixing 700 g stucco, 3.5 g of accelerator (finely ground gypsum), 10 g dry pregelatinized starch, 1.4 g sodium trimetaphosphate, 1 g chopped fiberglass, and vermiculite (see Table 5). Predetermined amounts of water corresponding to the amount required to form a water-to-stucco ratio of 1.4 were added to separate steel bowls. To each steel bowl was added 0.9 g dispersant and up to 2 drops of retarder. After the water solution reached room temperature, the steel bowl was installed under a Hobart mixer. The stucco mixture was added to the water solution and immediately mixed. Subsequently, the foam pump was activated and the form was injected into the bowl according to the predetermined injection rate. The foam injection time was pre-calculated to make boards with approximately 1600 lbs/MSF (see Table 6). After foam injection, the composition was mixed for an additional 5 seconds. The slurry was immediately poured into a premade paper envelop (made with 34 lbs/MSF newsline and 49 lbs/MSF manila paper), and cast by sandwiching between two aluminum plates that were spaced to make % inch boards. After casting, the boards were placed into an oven preset at 350° F. After 30 minutes, the boards were transferred to another oven that was preset at 110° F. The boards were left in the oven for two nights, and then removed from the oven and weighed. The dry boards were cut into samples of 6.625 inches×6.125 inches.

TABLE 6 Fire Endurance Index of Boards Comprising Vermiculite Board Fire Board Basis Form Endurance Vermiculite Weight Thickness Weight Density Injection Index Sample (lbs/MSF) WSR (g) (inches) (lbs/MSF) (lbs/ft³) Rate (sec) (min) 9 0 1.4 201.2 0.644 1573 29.3 18 55.1 10 25 1.4 201.8 0.645 1577 29.3 18 57.2 11 50 1.4 200.9 0.645 1570 29.2 18 57.8 12 75 1.4 204.5 0.647 1598 29.6 19 58.9 13 100 1.4 201.6 0.651 1576 29.1 19 56.0

Samples 9-13 were individually tested in the small-scale device (FIG. 2) to determine their respective FEI. Temperature traces for four samples are shown in FIG. 7, where time is plotted along the horizontal axis and temperature of the back-face of each sample is plotted along the vertical axis. In the graph of FIG. 7, line 311 represents the temperature trace for the control board (sample 9), line 312 represents the temperature trace for a board with 25 lbs/MSF vermiculite (sample 10), line 313 represents the temperature trace for a board with 50 lbs/MSF vermiculite (sample 11), line 314 represents the temperature trace for a board with 75 lbs/MSF (sample 12), and a “FEI” line 315 extends horizontally from a temperature of 315.6° C. (600° F.) to denote the FEI indexes for both samples.

As can be calculated from the graph of FIG. 7, the fire endurance index of the board comprising no vermiculite was 55.1 minutes (sample 9), 57.2 minutes for the board comprising 25 lbs/MSF vermiculite (sample 10), 57.8 minutes for the board comprising 50 lbs/MSF vermiculite (sample 11), 58.9 minutes for the board comprising 75 lbs/MSF vermiculite (sample 12), and 56.0 minutes for the board comprising 100 lbs/MSF vermiculite (sample 13). It was discovered that the board integrity was damaged when the sample comprised 100 lbs/MSF vermiculite (sample 13). The heat curves in FIG. 7 reveal, as the amount of vermiculite increases from zero to 75 lbs/MSF, the fire endurance index of the board increases from 55.1 minutes to 58.9 minutes. A further increase in vermiculite can damage the board integrity, thus compromising the fire endurance of the board.

This Example demonstrates that boards comprising a core made from slurries having a high water-to-stucco ratios combined with vermiculite can have even greater fire endurance.

The use of the terms “a” and “an” and “the” and “at least one” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term “at least one” followed by a list of one or more items (for example, “at least one of A and B”) is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Also, everywhere “comprising” (or its equivalent) is recited, the “comprising” is considered to incorporate “consisting essentially of” and “consisting of.” Thus, an embodiment “comprising” (an) element(s) supports embodiments “consisting essentially of” and “consisting of” the recited element(s). Everywhere “consisting essentially of” is recited is considered to incorporate “consisting of.” Thus, an embodiment “consisting essentially of” (an) element(s) supports embodiments “consisting of” the recited element(s). Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context. 

We claim:
 1. A fire resistant gypsum board comprising: a set gypsum composition disposed between two cover sheets, the set gypsum composition comprising an interlocking matrix of set gypsum formed from a slurry comprising at least stucco and water; the slurry having a water-to-stucco ratio from about 0.7 to about 2.0; and the board having a density from about 24 lbs/ft³ to about 40 lbs/ft³, and when at a thickness of about ⅝ inch, a nail pull resistance of at least about 70 lbs of force as determined according to ASTM C473-09, and a Fire Endurance Index (FEI) greater than about 52 minutes.
 2. The fire resistant gypsum board of claim 1, wherein the set gypsum composition comprises gelatinized starch in an amount greater than about 1% by weight based on the weight of the stucco.
 3. The fire resistant gypsum board of claim 1, wherein the set gypsum composition comprises a thickener.
 4. The fire resistant gypsum board of claim 3, wherein the thickener is silica fume, Portland cement, fly ash, clay, fine cellulosic particles, or a high molecular weight polymer, or any mixture thereof.
 5. The fire resistant gypsum board of claim 4, wherein the thickener is less than about 10% by weight based on the weight of the stucco.
 6. The fire resistant gypsum board of claim 4, wherein the high molecular weight polymer is polyacrylamide.
 7. The fire resistant gypsum board of claim 1, wherein the composition further comprises high thermal expansion particles.
 8. The fire resistant gypsum board of claim 7, wherein the high thermal expansion particles are vermiculite.
 9. The fire resistant gypsum board of claim 8, wherein vermiculite is less than about 5% by weight based on the weight of the stucco.
 10. The fire resistant gypsum board of claim 1, wherein the gypsum board has a board density from about 24 lbs/ft³ to about 33 lbs/ft³.
 11. The fire resistant gypsum board of claim 1, wherein the gypsum board has a thickness from about 0.25 inches to about 1.0 inches.
 12. The fire resistant gypsum board of claim 1, wherein the gypsum board has a thickness from about 0.59 inches to about 0.65 inches.
 13. The fire resistant gypsum board of claim 1, wherein the gypsum board has a Fire Endurance Index (FEI) at least 3 minutes greater than a board comprising set gypsum formed with a water-to-stucco ratio of less than about 0.7.
 14. The fire resistant gypsum board of claim 1, wherein the gypsum board has a Fire Endurance Index (FEI) at least 4 minutes greater than a board comprising set gypsum formed with a water-to-stucco ratio of less than about 0.7.
 15. The fire resistant gypsum board of claim 1, wherein when the board is built into a test assembly in accordance with UL U305, the board has a fire rating of at least about 55 minutes when heated in accordance with the time-temperature curve of ASTM standard E119-09.
 16. The fire resistant gypsum board of claim 1, wherein the board is built into a test assembly in accordance to UL U305, and has a fire rating of at least about 60 minutes when heated in accordance with the time-temperature curve of ASTM standard E119-09.
 17. The fire resistant gypsum board of claim 1, wherein when the board is built into a test assembly in accordance with UL U419, the board has a fire rating of at least about 60 minutes when heated in accordance with the time-temperature curve of ASTM standard E119-09.
 18. A fire resistant gypsum board comprising: a set gypsum composition disposed between two cover sheets, the set gypsum composition comprising an interlocking matrix of set gypsum formed from a slurry comprising at least stucco and water; the slurry having a water-to-stucco ratio from about 1.2 to about 2.0; the board having a density from about 24 lbs/ft³ to about 40 lbs/ft³, and when at a thickness of about % inch, a nail pull resistance of at least about 70 lbs of force as determined according to ASTM C473-09, and a Fire Endurance Index (FEI) greater than about 54 minutes.
 19. A method for making a fire resistant gypsum board comprising: forming a mixture of at least stucco and water, disposing the slurry on a first sheet, disposing a second sheet on the slurry to form a board preform having two cover sheets, cutting the board preform into a board of predetermined dimensions after the slurry has hardened sufficiently for cutting, and drying the board; the slurry having a water-to-stucco ratio from about 0.7 to about 2.0; the board when dried having a density from about 24 lbs/ft³ to about 40 lbs/ft³, and when at a thickness of about % inch, a nail pull resistance of at least about 70 lbs of force as determined according to ASTM C473-09, and a Fire Endurance Index (FEI) greater than about 52 minutes.
 20. The method of claim 19, wherein the water-to-stucco ratio is from about 1.2 to about 2.0. 